Winmodem

Main article: Softmodem

A PCI Winmodem/Softmodem (on the left) next to a traditional ISA modem (on the right). Notice the less complex circuitry of the modem on the left.
A Winmodem or Softmodem is a stripped-down modem for Windows that replaces tasks traditionally handled in hardware with software. In this case the modem is a simple digital signal processor designed to create sounds, or voltage variations, on the telephone line. Turn of the century computers often include a very simple card slot, the Communications and Networking Riser slot (CNR), to lower the cost of connecting it up. The CNR slot includes pins for sound, power and basic signaling, instead of the more expensive PCI slot normally used but the already low cost and almost universal applicability (unlike the CNR units which were restricted to machines that had such a slot) of the PCI winmodem meant that this was little used. Winmodems are cheaper than traditional modems, since they have fewer hardware components. One downside of a Winmodem is that the software generating the modem tones is not that simple, and the performance of the computer as a whole often suffers when it is being used. For online gaming this can be a real concern. Another problem with Winmodems is lack of flexibility, due to their strong tie to the underlying operating system. A given Winmodem might not be supported by other operating systems (such as Linux), because their manufacturers may neither support the other operating system nor provide enough technical data to create an equivalent driver. A Winmodem might not even work (or work well) with a later version of Microsoft Windows, if its driver turns out to be incompatible with that later version of the operating system.
Apple's GeoPort modems from the second half of the 1990s were similar, and are generally regarded as having been a bad move. Although a clever idea in theory, enabling the creation of more-powerful telephony applications, in practice the only programs created were simple answering-machine and fax software, hardly more advanced than their physical-world counterparts, and certainly more error-prone and cumbersome. The software was finicky and ate up significant processor time, and no longer functions in current operating system versions.
Today's modern audio modems (ITU-T V.92 standard) closely approach the Shannon capacity of the PSTN telephone channels they use. They are plug-and-play fax/data/voice modems.